One aspect of the invention relates to a trench transistor and to a method for fabricating a trench transistor.
Trench transistors have a semiconductor body, in which a trench structure and an electrode structure embedded in the trench structure are provided. The electrode structure is electrically insulated from the semiconductor body by means of an insulation structure. In the case of a field plate trench transistor, the electrode structure is divided into a gate electrode structure and a field electrode structure arranged below the gate electrode structure, in which case the field electrode structure may be electrically insulated from the gate electrode structure.
It is always an aim to further increase the integration density of the trench transistors. This may be effected, on the one hand, by reducing the distances between the individual trenches of the trench structure (that is to say that the width of that part of the semiconductor body which is situated between the trenches (“mesa zones”) is reduced). On the other hand, the width of the trenches themselves may be reduced. If use is made of the second possibility, that is to say that the width of the trenches is reduced, then it is generally necessary likewise to reduce the thickness of the insulation structure which electrically insulates the field electrode structure from the semiconductor body (since the reduction of the insulation structure thickness has a great “miniaturization potential”). This is problematic, however, since, in the case of excessively thin insulation layers between the field electrode structure and the semiconductor body, particularly in the case of fast switching operations, strong capacitive coupling effects occur between the drain/drift region of the trench transistor and the gate electrode structure (coupling of drain/drift region—field electrode structure—gate electrode structure) if the field electrode structure is electrically insulated from the gate electrode structure.